A new approach to the control of reaction stereochemistry is proposed. Radical cyclization reactions - a broadly applicable, potentially quite powerful approach to C-C bond construction - will be conducted within the hydrophobic receptor site of a new class of water-soluble hosts that have been designed and synthesized. Most importantly, the topography of the receptor site is matched to that of the reaction transition state - both are helical. This is an ideal arrangement for achieving high levels of enantioselection and diastereoselection. The methodology developed will be broadly applicable to the efficient synthesis of a wide range of structures of potential medicinal interest.